The incoming state Senate president has been forced to respond to turmoil about accusations that his domestic partner mocked outgoing Senate President Therese Murray on social media and boasted to senators about his influence on key decisions on Beacon Hill.

After hearing from several of his colleagues and advisers, Stanley Rosenberg instructed his partner, Bryon Hefner, 27, a public relations executive and former Senate aide, to cease talking with other senators about committee assignments, leadership positions, and staffing.

According to Beacon Hill officials who have direct knowledge of his activities, Hefner has spoken openly about the influence he expects to wield, assuming Rosenberg, 65, a Beacon Hill legislative veteran, wins the presidency in early January.

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Further, Rosenberg acknowledged that Murray had conveyed concerns to him about tweets that mocked and disparaged her and insulted several other state officials and leading political officials — and said she was convinced Hefner was responsible.

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Rosenberg said in a Nov. 26 interview that he was made aware of some of Hefner’s behavior by other senators and acknowledged that he had admonished his partner. He said he has made it clear to Hefner that he is not to be involved in the business of the Senate.

“Very clearly, very specifically, he’s not involved in making any of the decisions,” the Amherst Democrat said. “All personnel decisions, all the chairmanships, are going though the normal internal processes.”

Murray declined to comment on the situation. Hefner declined interview requests and did not respond to written questions from the Globe.

The dust-up about Hefner’s activities has raised concern among Rosenberg’s supporters who fear that, if
his partner’s actions are not checked, his election as Senate president could be derailed. Rosenberg’s agreement to be interviewed on the sensitive subject suggests he wanted to send a signal to his colleagues that he has put an end to Hefner’s interference in the Senate’s internal affairs and any use of social media to ridicule political figures.

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One Twitter account, whose ownership could not be independently verified, posted several tweets that drew complaints. One tweet, on June 5, displayed a photo of Murray wearing a witch’s hat and holding a broom, depicting her as the Wicked Witch of the West from “Wizard of Oz.’’ In the background is Rosenberg appearing as a monkey. Under the photo is a caption: “Wicked: The Untold Story of the Bitch of Beacon Hill.”

Another tweet is a photo of an inebriated-looking woman (not Murray) holding a cocktail glass and a bottle, with the title, “We Love You Madame President.”

From a separate account, Hefner tweeted a photo of himself posed with Republican gubernatorial candidate Charlie Baker; Baker’s wife, Lauren; and his running mate, Karyn Polito, during the fall campaign, as Senate Democrats faced what could have been historic losses within their own caucus. That sparked a kerfuffle within the Democratic ranks and, Rosenberg said, even prompted a complaining phone call to him from Senator Thomas M. McGee, the Lynn Democrat and chairman of the state Democratic Party.

Last spring, Murray confronted Rosenberg, whom she has groomed to take over her position, about the tweets, prompting Rosenberg to order his partner to shut down the social media page.

“She told me that there were social media posts that she was concerned about and were offensive and that needed to stop,’’ Rosenberg said. “I turned to Bryon and said, ‘I understand there are some social media things you have put up that are offensive to people and inappropriate. Stop.’ ”

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He said he learned of the postings “weeks” after they appeared, but he never saw them.

‘[Therese Murray] told me that there were social media posts that she was concerned about.’

He also discounted the concern that Hefner’s behavior threatened his ability to take over the Senate presidency.

“I am not aware of this dynamic to the extent you are describing,’’ he said in his Globe interview. “I am aware two people spoke to me about social media concerns, but it is being presented to me now as though it is a significantly larger problem than has been brought [to] my attention.”

Despite the political headaches Hefner has created for Rosenberg, he gave a poignant defense of his domestic partner, who helped him battle cancer.

“We are in a deeply committed relationship,’’ Rosenberg said when asked whether he and Hefner planned to get married. “The future is open. It is like everybody else. If you get there, you get there, and you get there on your own terms and in your own time. I have that right as a human being.”

Rosenberg, who first came to Beacon Hill as a state representative in 1987, said Hefner’s presence in his life led him to publicly disclose his sexual identity after years of hiding it.

“It was very difficult getting to this point in my life, frankly, to actually have relationships, and he actually brought me to the dance, if you will,’’ Rosenberg said, speaking haltingly and with emotion. “I would not have come out if he had not come into my life. It was the greatest gift anyone has given to me.”

Rosenberg’s election to head the Senate would be a historic marker. He would be the first openly gay legislative leader in Massachusetts.

Hefner, whose bond to Rosenberg is related in part to their shared background as foster children, met the senator when he got a job in his State House office several years ago. Rosenberg, currently the Senate majority leader, said before their close relationship developed, Hefner left his payroll.

Hefner landed a job at Regan Communications in May as a public relations executive. The high-profile firm is owned by George Regan, the one-time press secretary to the late Boston mayor Kevin White.